A few suggestions:
- Since ANY above the fold element can be potentially elected, perhaps "Hero Element" is a bit misleading, perhaps using the term "Visible Critical Element" would be better?

- Could there be a way to assign a different shading to the hero element / element components (ex: the multiple images and code that may make up a hero carousel, for example) in the page waterfall so that users can identify at a glance where the Hero Element falls within the page waterfall and what that particular element might be on a given page?